In modern internal combustion engines, devices for variably adjusting the timing of gas exchange valves are used to enable variable configuration of the phase position of a camshaft relative to a crankshaft within a defined angular range between a maximum advanced position and a maximum retarded position. For this purpose, a hydraulic phase adjustment unit of the device is integrated into a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train can be implemented for example as a belt, chain or gear drive. The phase adjustment speed and the pressure medium requirement are significant parameters of such devices. To enable the phase position to be adapted in an optimum manner to the various driving situations, high phase adjustment speeds are desirable. In the context of measures for reducing consumption, there is furthermore a demand for an ever smaller pressure medium requirement so as to enable the pressure medium pump of the internal combustion engine to be of smaller design or to enable the delivery rate to be reduced when using regulated pressure medium pumps.
A device of this type is known for example from EP 0 806 550 A1. The device comprises a vane-type phase adjustment unit with a drive input element, which is in drive connection with the crankshaft, and a drive output element, which is connected to the camshaft for conjoint rotation therewith. A plurality of pressure spaces is formed within the phase adjustment unit, wherein each of the pressure spaces is divided into two oppositely acting pressure chambers by means of a vane. The vanes are moved within the pressure spaces by means of a supply of pressure medium to or discharge of pressure medium from the pressure chambers, which brings about a change in the phase position between the drive output element and the drive input element. In this case, the pressure medium required for phase adjustment is provided by a pressure medium pump of the internal combustion engine and is directed selectively to the advance or retardation chambers by means of a control valve. The pressure medium flowing out of the phase adjustment unit is directed into a pressure medium reservoir, the oil sump of the internal combustion engine. Phase adjustment is thus accomplished by means of the system pressure provided by the pressure medium pump of the internal combustion engine.
A further device is known for example from U.S. Pat. No. 5,107,804 A. In this embodiment, the phase adjustment unit is likewise of the vane type, and a plurality of advance and retardation chambers is provided. In contrast to EP 0 806 550 A1, phase adjustment is not accomplished by supplying pressure medium to the pressure chambers by means of a pressure medium pump; instead, alternating moments acting on the camshaft are used. The alternating moments are caused by the rolling movements of the cams on the gas exchange valves, each of which is preloaded by a valve spring. In this case, the rotary motion of the camshaft is braked during the opening of the gas exchange valves and accelerated during closure. These alternating moments are transmitted to the phase adjustment unit, with the result that the vanes are periodically subjected to a force in the direction of the retardation stop and of the advance stop. As a result, pressure peaks are produced alternately in the advance chambers and the retardation chambers. If the phase position is supposed to be held constant, pressure medium is prevented from flowing out of the pressure chambers. In the case of a phase adjustment in the direction of earlier timing, pressure medium is prevented from flowing out of the advance chambers, even at times at which pressure peaks are being produced in the advance chambers. If the pressure in the retardation chambers rises owing to the alternating moments, this pressure is used to direct pressure medium out of the retardation chambers into the advance chambers, using the pressure of the pressure peak generated. Phase adjustment in the direction of later timing is accomplished in a similar way. In addition, the pressure chambers are connected to a pressure medium pump, although only to compensate for leaks from the phase adjustment unit. Phase adjustment is thus accomplished by diverting pressure medium out of the pressure chambers to be emptied into the pressure chambers to be filled, using the pressure of the pressure peak generated.
Another device is known from US 2009/0133652 A1. In this embodiment, phase adjustment in the case of small alternating moments is accomplished, in a manner similar to the device in EP 0 806 550 A1, by supplying pressure to the advance chambers or the retardation chambers by means of a pressure medium pump while simultaneously allowing pressure medium to flow out of the other pressure chambers to the oil sump of the internal combustion engine. In the case of high alternating moments, these are used, as in the device in U.S. Pat. No. 5,107,804 A, to direct the pressure medium under high pressure out of the advance chambers (retardation chambers) into the retardation chambers (advance chambers). During this process, the pressure medium expelled from the pressure chambers is fed back to a control valve, which controls the supply of pressure medium to or discharge of pressure medium from the pressure chambers. The pressure medium passes via check valves within the control valve to the inlet port, which is connected to the pressure medium pump, wherein some of the pressure medium is expelled into the pressure medium reservoir of the internal combustion engine.
EP 2 075 421 A1 discloses a valve for a camshaft adjuster. The valve comprises a valve piston which is arranged in a rotatable manner in a valve housing. Inlets and outlets for pressurized oil are arranged such that, by adjusting the valve piston, pressurized oil can be conducted to the adjustment chambers and to a locking mechanism. Here, the locking mechanism can be activated not only in an end position of the camshaft adjuster, that is to say at a stop in the retarded or advanced position, but also in an intermediate position. This permits mid-position locking, which may be expedient depending on the engine application.
DE 198 50 947 presents a device for controlling the timing of an internal combustion engine, having at least one drive means, at least one camshaft with cams, at least one hydraulically actuable adjustment unit for adjusting the angle of relative rotation between the drive means and the camshaft, at least one hydraulic fluid supply device for charging the adjustment unit, and at least one positive control unit by means of which the hydraulic charging of the adjustment unit can be influenced at least at times and/or at least in part as a function of the absolute angle of rotation of the camshaft and/or of the cams. Here, a flow connection to the adjustment chambers is shut off in a targeted manner when pressure fluctuations caused by torques arise which would be imparted back to the adjustment chambers by the camshaft when cams are running on or running off.
U.S. Pat. No. 6,186,104 B1 discloses a vane-type valve timing control device for an internal combustion engine, in which, between the pressure cells and the control valve which actuates them, there is connected a pressure distributor device which serves to suppress disturbance camshaft torques. For this purpose, for example during a retardation, the oil supply to the pressure cells is shut off when an advance torque arises. Conversely, during an advance, the oil supply to the pressure cells is shut off when a retardation torque arises. Similarly to DE 198 50 947, therefore, a return swing of the adjustment unit is suppressed owing to the adjustment of opposing camshaft torques.